Filtration respirators or face masks are used in a wide variety of applications when it is desired to protect a human's respiratory system from particles suspended in the air or from unpleasant or noxious gases. Generally such respirators or face masks are of one of two types—a molded cup-shaped form or a flat-folded form. The flat-folded form has advantages in that it can be carried in a wearer's pocket until needed and re-folded flat to keep the inside clean between wearings.
The flat-folded form of face mask has been constructed as a fabric which is rectangular in form and has pleats running generally parallel to the mouth of the wearer. Such constructions may have a stiffening element to hold the face mask away from contact with the wearer's face. Stiffening has also been provided by fusing a pleat across the width of the face mask in a laminated structure or by providing a seam across the width of the face mask.
Also disclosed is a pleated respirator which is centrally folded in the horizontal direction to form upper and lower opposed faces. The respirator has at least one horizontal pleat essentially central to the opposed faces to foreshorten the filter medium in the vertical dimension and at least one additional horizontal pleat in each of these opposed faces. The central pleat is shorter in the horizontal dimension relative to the pleats in the opposed faces which are shorter in the  horizontal dimension relative to the maximum horizontal dimension of the filter medium. The central pleat together with the pleats in opposed faces form a self-supporting pocket.
Also disclosed is a respirator made from a pocket of flexible filtering sheet material having a generally tapering shape with an open edge at the larger end of the pocket and a closed end at the smaller end of the pocket. The closed end of the pocket is formed with fold lines defining a generally quadrilateral surface comprising triangular surfaces which are folded to extend inwardly of the pocket, the triangular surfaces facing each other and being in use, relatively inclined to each other.
More complex configurations which have been disclosed include a cup-shaped filtering facepiece made from a pocket of filtering sheet material having opposed side walls, a generally tapering shape with an open end at the larger end and a closed end at the smaller end. The edge of the pocket at the closed end is outwardly bowed, e.g. defined by intersecting straight lines and/or curved lines, and the closed end is provided with fold lines defining a surface which is folded inwardly of the closed end of the pocket to define a generally conical inwardly extending recess for rigidifying the pocket against collapse against the face of the wearer on inhalation.
Further disclosed is face mask having an upper part and a lower part with a generally central part therebetween. The central part of the body portion is folded backwardly about a vertical crease or fold line which substantially divides it in half. This fold or crease line, when the mask is worn, is more or less aligned with an imaginary vertical line passing through the center of the forehead, the nose and the center of the mouth. The upper part of the body portion extends upwardly at an angle from the upper edge of the central part so that its upper edge contacts the bridge of the nose and the cheekbone area of the face. The lower part of the body portion extends downwardly and in the direction of the throat form the lower edge of the center part so as to provide coverage underneath the chin of the wearer. The mask overlies, but does not directly contact, the lips and mouth of the wearer. 